Vibration and noise are two significant customer complaint areas for home appliances such as clothes washing machines. In many cases, these two complaints are linked—excess vibration often leading to excess noise.
One source of vibration and noise can be side panels attached to each side of a washing machine. Side panels are commonly made of sheet metal and attached to the frame of the washing machine at the edges and/or corners of the panels. A vibration response pattern of a side panel may have several peaks, each peak representing a resonant or natural frequency of the side panel. By convention, the “first natural frequency” is the lowest natural frequency of the side panel. Likewise, the second natural frequency is the second lowest natural frequency, and so on. Operating the washing machine at a frequency near one of the side panel natural frequencies can result in a large resonant vibration response by the side panel.
In a washing machine, the primary driving frequency is created by the rotation of a drum (or tub) holding clothes inside the washing machine. The operating frequency of the washing machine is equivalent to the rotational frequency of the drum during operation. During a high-speed spin cycle, the rotational frequency of the drum may range from 0 Hz to 20 Hz or more. In that case, the rotational frequency of the drum may pass through one or more natural frequencies of the side panel, thus, causing resonant vibration.
One solution is to set the maximum operational frequency at a non resonant value, and, at the beginning of the spin cycle, quickly accelerate to the maximum operating frequency (thus, passing through the side panel natural frequencies). However, this approach still results in some resonant vibration. Additionally, in a high-speed spin cycle, the operating frequency may pass through several side panel frequencies, leading to further vibration.
Dampers and other shock absorbers can be helpful in reducing vibration and noise. However, those solutions require additional components and add weight to the washing machine. Minor additional structural stiffening has also been rejected because it was thought that increasing the first natural frequency of the side panel would cause the washing machine to pass through side panel resonance at a higher, more damaging speed.
Thus, a need exists for a washing machine side panel with a natural frequency that is significantly different from any operating frequency of the washing machine. Washing machines require many parts and are expensive to manufacture. It is therefore also desirable to have a lightweight, easily manufactured, and inexpensive means of reducing side panel vibration without increasing the number of components. Finally, side panel looseness or slack can also contribute to vibration, noise, and other problems. Thus, a further need exists for side panels with reduced looseness or slack.
Although these problems have been described in terms of clothes washing machines, other appliances also exhibit side panel vibration. For example, fabric driers, dish washers, standalone fans, appliances with incorporated fans, combination fabric care appliances and other devices may benefit from additional side panel vibration control.